How can you say your needs don't really change when technology changes every year? If true, wouldn't you still be using a phone from say 2 years ago? As for extra battery, the Note 4's is extremely portable, smaller and thinner than a wallet. Imo, much more efficient and convenient than to be tethered.
I bought the extra battery and charger for my Note 4 when I knew I was going to Star Wars Celebration (back in April). I knew outlet space would be a hot commodity and plugging in when on the convention floor would be a rarity. So, I was thinking ahead. Carrying around the extra battery was a savior.
Standing in some of those insane lines, some times all I had to entertain myself was my phone. Of the 4 days at the convention, I swapped out the battery three times.
Since April, I've been keeping up with the extra battery and if I know I'm going to be out (a lot) I bring it with me.
I've also been playing Ingress since the end of June -- when I turn on the GPS/location it drains the battery faster. I turn it off when I'm not playing. So, it's nice to have an extra battery.
When I get the Note 5, I'll probably have to invest in a good power pack.